We use the Marquis, Mecke, Mandelin, and Simon reagents for testing (pictured below). These reagents work by reacting with substance to give one of several characterized reactions.
The reagents have the following reactions in the table below. These are the main things we look for when testing, however the kits are able to test for more substances then are listed in the table below. (the listed ones just include the most common things people come across)